Today I woke up and all the headlines in my health science bubble were about how suddenty, again, soy is the new health food. Funny, just last month it was the demon responsible for low sperm count and premature puberty in children.
What gives: is soy healthy or not?
The health effects of soy are complicated. Why? Because when we look at populations of people that historically eat more soy—such as those living in Asia— they are typically healthier than those who eat a typical American diet. And they eat more soy. A 2017 study on the negative effects of BPA on fertility, demonstrated that those women who had diets that included soy had better fertility treatment outcomes. Yet, when we study soy and its effects in rats, particularly its effects during pregnancy, there are links to soy and a number of negative health outcomes including lower sperm count, premature onset of puberty, and even may effect normal brain growth. The concern became so great that the AAP has advised that infants only be fed soy formula if medically necessary. Restrictions on soy formula and soy food for infants and children have been proposed or passed in France, Israel, and the United Kingdom.
Research does provide some clues to this disparity of why soy can be both health in some cases and unhealthy in others. One answer is quantity and quality: Asian cultures didn’t eat as much soy as originally presumed and ate more of that soy fermented—nato, miso, and tempeh—which all have less of the anti-nutrients of soy and more of the beneficial properties. The other answer for why we can’t figure out once and for all if soy is healthy is based on its estrogenic properties. We know that soy isoflavones bind and activate estrogen receptors in the body. The soy isoflavones are weaker than estrogen binders than estrogen or, seemingly, some of the other chemical estrogen-mimickers such as BPA.
The phytoestrogens in soy have been show to negatively affect reproduction and endocrine function and can contribute to thyroid problems (which are linked to infertility and miscarriage). As well, soy can reduce the assimilation of minerals such as calcium, magnesium, copper, and iron and interfere with the body’s absorption of Vitamin B12, D, and protein. As well it can contain high levels of aluminum, a known neurotoxin.
Men who ate or drank soy were more likely to have lower sperm counts: the equivalent of one cup of soy milk per day associated with 50% lower sperm count than that of men who didn’t eat soy, according to a 2008 study at the Harvard Public School of Health. One study linked a woman’s consumption of soy in utero to increased chances of the child developing leukaemia and others with infant boys being born with the male genital disorder hypospadias: although both results may be attributed more to the pesticides used in growing soy.
If you are a man interested enhancing your fertility, a child, a pregnant woman, or a woman that works hard to limit your exposure to environmental estrogens: the research suggests that typical soy is not for you. Perhaps, however, if you are a woman with high environmental estrogen exposure—such as from plastics like BPA—maybe soy is a lesser evil. Although, I’d personally start by reducing my BPA exposure.
It’s hard to get too excited about lesser evils, but it does help me feel better about enjoying a little fried tofu every now and then.
Read the Science on Soy
Barrett JR. The Science of Soy: What Do We Really Know? Environmental Health Perspectives. 2006;114(6):A352-A358.
Chavarro, Jorge E. et al. “Soy Intake Modifies the Relation Between Urinary Bisphenol A Concentrations and Pregnancy Outcomes Among Women Undergoing Assisted Reproduction.” The Journal of Clinical Endocrinology & Metabolism, 2016; jc.2015-3473 DOI: 10.1210/jc.2015-3473
Chavarro, Jorge E., Thomas L. Toth, Sonita M. Sadio, and Russ Hauser. “Soy food and isoflavone intake in relation to semen quality parameters among men from an infertility clinic” Hum. Reprod. (2008) 23 (11): 2584-2590. doi: 10.1093/humrep/den243
Cole, William, “11 Everyday Toxins That Are Harming Your Thyroid” MindBodyGreen online. January 21, 2014. Accessed December 4, 2016.
Conrad S and others. Soy formula complicates management of congenital hypothyroidism. Archives of Disease in Childhood 2004 Jan;89(1):37-40.
Daniel, Kaayla T. “The Whole Soy Story: The Dark Side of America’s Favorite Health Food” (New Trends, 2005). 153-170.
North K and Golding J. A maternal vegetarian diet in pregnancy is associated with hypospadias. The ALSPAC Study Team. Avon Longitudinal Study of Pregnancy and Childhood. BJU Int 2000 Jan;85(1):107-113.
The Raine Study: Western Australia Pregnancy Cohort. Studying 2900 pregnant women and the health of their children over 27 years. Over 300 published studies available at http://rainestudy.production1.claritycommunications.com.au/research-findings/publications/
Strick R, Strissel PL et al. Dietary bioflavonids induce cleavage in the MLL gene and may contribute to infant leukemia. Proc Natl Acad Sci USA, 2000, 25,97, 9, 4790-95.
Ross JA, Potter JD et al. Maternal exposure to potential inhibitors of DNA topoisomerase II and infant leukemia (United States) a report from the Children’s Cancer Group, Cancer Causes Control, 1996,7, 581-590.
Vilela, ML, Willingham E, Buckley J, Liu BC, Agras K, Shiroyanagi Y, Baskin LS. “Endocrine disruptors and hypospadias: role of genistein and the fungicide vinclozolin.” Urology. 2007 Sep;70(3):618-21.
Strom BL and others. Exposure to soy-based formula in infancy and endocrinological and reproductive outcomes in young adulthood. JAMA 2001 Nov 21;286(19):2402-3.